Tuesday, January 03, 2006

heavy heat

a masonry stove

how are we going to heat? this question has come up more often recently. i'm pretty sure we're agreed that we'll use wood for fuel. we have 165 acres of wooded land, so it makes sense economically and ecologically to harvest wood from our own land. there is enough fallen timber each year to supply us with all the firewood we'll need.

i've been looking into masonry stoves as one option. the other options would be a cast iron woodstove and or a wood fired boiler of some sort. the latter would require electricity to pump the water around. a combination of all of the above might also be possible.

masonry stoves—one is pictured—have many advantages. they require firing just once a day if built properly, perhaps twice in extremely cold weather. they can heat hot water. they can be built with oven cavities for baking bread and the like. the surface of the stove is never hot enough to burn and provides even heat through the day. they absorb solar energy during the day and re-radiate it at night. in the summer, if not fired, they can help cool. if operated properly, they rarely, if ever, need cleaning. they produce very little pollution and almost no smoke.

disadvantages are few, as far as i can see, but might include the following: they're massive, requiring substantial foundations to support them. they don't respond to variations in weather quickly. once the stove is fired, you're in for an 18 hour trip with it. wood has to be split to no larger than 3" in diameter so that it burns fast and hot. a masonry stove has to be built, whereas a cast iron stove is simply put in place.

for destiny, i imagine a masonry stove might be placed as part of the divider between the kitchen and open space, as a centerpiece to the building, with baking ports on the kitchen side. it would provide warmth to the whole building by being in the center, although being in the kitchen might make it too hot with stoves going. but, windows can always be opened. masonry stoves can be highly efficient, and until the addition of catalyitic converters on woodstoves were probably the most efficient means of heating with wood.

i'd like to think we could build a masonry stove ourselves, but it may be beyond our skills. one possibility would be to hire a mason to work with us and teach us how to build one. there are also cast iron kits available that one builds around. these are designed for self-installation.

masonry stoves achieve their efficiency by burning nearly completely all the combustible material in wood. they can fire as hot as 2000 degrees, unlike a conventional woodstove that operates between 200 and 500 degrees. the minimum temperature for burning wood completely is about 1200 degrees. because cast iron communicates heat so well, a 1200 degree fire in a cast iron stove creates dangerous and uncomfortable situation, not only because at such high temperatures things nearby would tend to ignite but also because the cast iron begins to lose its structural properties. a masonry stove, on the other hand, is a slow communicator of heat. masonry stoves insulate and trap the heat of the fire so as much of the energy release by combustion is absorbed into the masonry. inside most stoves is a long and circuitous flue that exposes a large surface area of masonry to escaping combustion gases. gases rising up the chimney are usually a fraction of the firebox temperature because so much energy has been absorbed and, if properly combusted, contain no creosote which can build on chimney walls with cast iron stoves creating a potential fire hazard. once absorbed, the 1200-2000 degree heat makes its way to the outside of the stove over a period of many hours where it is radiated into the room at safe and comfortable temperatures. many masonry stoves are designed with built-in benches or beds to provide comfortable sitting and sleeping in cold months.

technical considerations aside, masonry stoves feel great. their mass provides an anchor to a room, the warmth is smooth and constant and a stove can integrate with the building unlike any other heating system. a masonry stove might be a good option for the bathhouse as well as the kitchen.

4 Comments:

i think this will probably be like the flush toilet. if there is a will there is a way. i looked into the masonry stoves at the request of several people who have mentioned them to me over the past year or so.

for many reasons, after researching them, i think they would be our best choice ecologically and economically.

the thing that really sold me on them was their safety. it would be very difficult to burn the place down with a masonry stove, which can safely withstand blistering temperatures. not so with a cast iron stove. for example, actworth, new hampshire reports that 80% of winter structure fires there are due to improper woodstove maintenance or operation.

a masonry stove is something that should be built by an experienced mason. If you want to learn how to lay bricks, build a low garden wall. Brick layers go to school. The Stove your talking about is a massive and complicated structure. look for a good mason.

You could have the opening for the wood feed on the living room side of the stove and the oven portals on the kitchen side. There's no reason they have to be on the same side.Also by stair stepping the Kitchen side you can create more cooking area with varied temperatures. Consider insetting iron plates on the tops of ledges to conduct more heat for water pots.

i'd like to see a stove (masonry or otherwise) in the center of the room or as a divider between kitchen and dining/open space. the design i saw on the website shows a stove against an outside wall, and this doesn't make much sense in a cold climate as you want all the heat generated to stay in the room. centrally locating the stove will provide the most heat efficiency as far as I can tell.